Chlorine resistant polyamides and membranes made from the same

ABSTRACT

A chlorine resistant polyamide is formed from the reaction product of an amine and an acid chloride monomer wherein the acid chloride monomer is modified with electron-withdrawing groups that exhibit sufficient activity to (i) minimize any chlorination on both the amine and acid chloride side and (ii) minimize N-chlorination. A membrane is made from the polyamide and, in one application, the membrane is used in a desalination unit.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. patent application Ser. No. 11/746,140,filed May 9, 2007, now issued as U.S. Pat. No. ______ on ______, hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to chlorine resistant polymers and tomembranes made from such polymers such as are used, for example, asdesalting membranes for water treatment systems.

BACKGROUND OF THE INVENTION

Presently, the desalting membrane of choice worldwide is the polyamide(PA) membrane. In general, PA membranes are made by forming a thin PAfilm on the finely porous surface of a polysulfone (PS) supportingmembrane by an interfacial reaction between the reactant pair trimesoylchloride (TMS) and m-phenylenediamine (MPD). The following equationillustrates the chemical formation of the PA desalination barrier.

In this equation, the first term represents m-phenylenediamine in water,the second term represents the trimesoyl chloride in hydrocarbon, andthe resultant term represents the fully aromatic polyamide thin film.This is the equation for the PA thin-film composite membrane developedby Cadotte and others (see, e.g., J. E. Cadotte, J. J. Peterson, R. E.Larson and E. E. Erickson, “A new thin-film composite seawater reverseosmosis membrane,” Desalination, 32, 25-31 (1980)) and, as indicatedabove, is the membrane in common use throughout the world.

A great need exists to improve the stability of the presentstate-of-the-art membranes used for chlorine disinfection. Suchimprovement is critical for Reverse Osmosis (RO) plants operating onwastewaters, surface waters and open seawater intakes whereindisinfection by chlorination is required to control the growth ofmicroorganisms (so-called “biofouling”) on the surface of the membrane.These PA membranes are so susceptible to deterioration by chlorine thatdechlorination is required when chlorine is used as a disinfectant inthe pretreatment. It will be understood that dechlorination prior to thePA membrane creates additional costs and effectively nullifiesdisinfection on the membrane surface where disinfection is needed. It isalso noted that such dechlorination does not neutralize all chlorine,and the small amount of residual chlorine shortens membrane life.

It will be appreciated that there is a serious need for achlorine-resistant PA membrane since such membrane would havesignificantly increased life, would prevent biofouling and lower theoverall cost of desalting. In spite of claims by some manufacturers thattheir membranes last longer than competitive membranes in lowconcentrations of chlorine, it has been found that all of these PAmembranes degrade and lack chemical stability to oxidants such aschlorine. However, as indicated above, chlorine is very effectivebiocide in water treatment and thus its use is quite desirable. If atruly effective chlorine resistant membrane could be provided, desaltingplants and mobile desalting units could operate in a more robust manner,while decreasing costs of membrane cleaning, storage and replacement andof general overall operations.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an acid chloride monomer suchas that discussed above is modified by the addition of certain chemicalgroups to produce a chlorine resistant polyamide. Further, and quiteimportantly, a resultant membrane employing this polyamide is providedwhich, in addition to being chlorine resistant, has very desirabletransport properties as discussed in more detail below. In general, oneaspect of the invention involves modifying the acid side, i.e., the acidchloride, with electron-withdrawing groups that are active enough tominimize ring chlorination on both the amine and acid and to alsominimize N-chlorination.

According a further aspect of the invention, there is provided achlorine resistant polyamide comprising the reaction product of an amineand an acid chloride monomer wherein the acid chloride monomer ismodified with electron-withdrawing groups that exhibit sufficientactivity to (i) minimize any chlorination on both the amine and acidchloride side and (ii) minimize N-chlorination.

In one preferred embodiment, the acid chloride monomer comprisesmonofluorotrimesoyl chloride.

In another preferred embodiment, the acid chloride monomer comprisesperfluorotrimesoyl chloride.

In yet another preferred embodiment, the acid chloride monomer comprisesnitrotrimesoyl chloride.

In a further preferred embodiment, the acid chloride monomer comprisesperchlorotrimesoyl chloride.

In another preferred embodiment, the acid chloride monomer comprises1,3,5-benzenetri-(difluoroacetoyl chloride).

Different amines may be used and in one embodiment, the amine comprisem-phenylenediamine.

In a further embodiment, the amine comprises 1,3,5-triaminobenzene.

In yet another embodiment, the amine comprises1,2,4,5-tetraaminobenzene.

In a further embodiment, the amine comprises1,2,3,4-tetraaminocyclohexane.

In another embodiment, the amine comprises tetrakis (aminomethyl)methane.

In yet another embodiment, the amine comprises a mixture of two or moreof the foregoing amines.

In accordance with a further aspect of the invention there is provided achlorine resistant membrane including a chlorine resistant polyamidecomprising the reaction product of an amine and an acid chloride monomerwherein the acid chloride monomer is modified with electron-withdrawinggroups that exhibit sufficient activity to (i) minimize any chlorinationon both the amine and acid chloride side and (ii) minimizeN-chlorination.

As set forth above for the polyamide, in one preferred embodiment theacid chloride monomer comprises monofluorotrimesoyl chloride, while inother preferred embodiments, the acid chloride monomer comprisesperfluorotrimesoyl chloride or nitrotrimesoyl chloride orperchlorotrimesoyl chloride or 1,3,5-benzenetri-(difluoroacetoylchloride).

Also as set forth above, the amine preferably comprises an amineselected from the group consisting of m-phenylenediamine,1,3,5-triaminobenzene, 1,2,4,5-tetraaminobenzene,1,2,3,4-tetraaminocyclohexane, tetrakis (aminomethyl) methane, andmixtures thereof.

According to a further aspect of the invention, there is provided areverse osmosis desalination unit comprising a membrane support and,mounted on the membrane support, a chlorine resistant membrane includinga chlorine resistant polyamide comprising the reaction product of anamine and an acid chloride monomer wherein the acid chloride monomer ismodified with electron-withdrawing groups that exhibit sufficientactivity to (i) minimize any chlorination on both the amine and acidchloride side and (ii) minimize N-chlorination.

As set forth above, the acid chloride monomer preferably comprises oneof monofluorotrimesoyl chloride, perfluorotrimesoyl chloride,nitrotrimesoyl chloride, perchlorotrimesoyl chloride, and1,3,5-benzenetri-(difluoroacetoyl chloride).

As was also set forth above, the amine preferably comprises an amineselected from the group consisting of m-phenylenediamine,1,3,5-triaminobenzene, 1,2,4,5-tetraaminobenzene,1,2,3,4-tetraaminocyclohexane, tetrakis (aminomethyl) methane, andmixtures thereof.

In accordance with a further aspect of the invention, there is provideda chlorine resistant polyamine comprising the reaction product of anamine and an acid chloride selected from the group consisting ofmonofluorotrimesoyl chloride, perfluorortrimesoyl chloride,nitrotrimesoyl chloride, perchlorotrimesoyl chloride and1,3,5-benzenetri-(difluoroacetoyl chloride). In one preferredembodiment, the acid chloride comprises monofluorotrimesoyl chloride.

Preferably, the amine is selected from the group consisting ofm-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4,5-tetraaminobenzene,1,2,3,4-tetraaminocyclohexane, tetrakis (aminomethyl) methane, andmixtures thereof.

According to yet another aspect of the invention, there is provided achlorine resistant membrane including a chlorine resistant polyamidecomprising the reaction product of an amine and an acid chlorideselected from the group consisting of monofluorotrimesoyl chloride,perfluorortrimesoyl chloride, nitrotrimesoyl chloride,perchlorotrimesoyl chloride and 1,3,5-benzenetri-(difluoroacetoylchloride). In one preferred embodiment, the acid chloride comprisesmonofluorotrimesoyl chloride.

Preferably, the amine is selected from the group consisting ofm-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4,5-tetraaminobenzene,1,2,3,4-tetraaminocyclohexane, tetrakis (aminomethyl) methane, andmixtures thereof.

According to a further aspect of the invention, there is provided areverse osmosis desalination unit comprises a membrane support and,supported on the membrane support, a chlorine resistant membranecomprising the reaction product of an amine and an acid chlorideselected from the group consisting monofluorotrimesoyl chloride,perfluorotrimesoyl chloride, nitrotrimesoyl chloride, perchlorotrimesoylchloride and 1,3,5-benzenetri-(difluoroacetoyl chloride). In onepreferred embodiment, the acid chloride comprise monofluorotrimesoylchloride.

As above, the acid chloride preferably comprises the amine selected fromthe group consisting of m-phenylenediamine, 1,3,5-triaminobenzene,1,2,4,5-tetraaminobenzene, 1,2,3,4-tetraaminocyclohexane, tetrakis(aminomethyl) methane and mixtures thereof.

Further features and advantages of the present invention will be setforth in, or apparent from, the detailed description of preferredembodiments thereof which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 are graphs used in comparing the water flux and saltrejection characteristics, respectively, of membranes constructed inaccordance with one aspect of the invention with prior art referencemembranes or controls; and

FIG. 3 is a perspective view of a desalination membrane unit.

DETAILED DESCRIPTION

As indicated above, generally speaking, one aspect of the inventionconcerns modifying the acid chloride (TMC) of a TMC/MPD polyamide withelectron-withdrawing groups that are reactive enough to minimize ringchlorination on both the acid (TMC) and amine (MPD) side and to minimizeN-chlorination as well. In addition, to electron-withdrawing, thesechemical groups must have the correct p orbitals or π system forresonance to occur, must be spatially small in size so they do notinterfere in the polymerization process, must be non-ionizing (thusresulting in changes to the acid chloride compound favorable regardingsolubility in hexane), and must be fairly straightforward to synthesizefrom commercially available precursors so the final cost of the compoundis not unfavorable.

The five compounds described below have been found to be effective. Thefirst is represented as follows:

This compound is monofluorotrimesoyl chloride (MFTMC), and is notavailable commercially, but has been synthesized by the applicants.Based on current studies, this is a preferred embodiment of the chemicalgroups.

A further useful compound is represented as follows:

This compound is perfluorotrimesoyl chloride (PFTMC), and is notavailable commercially.

A third compound is represented as follows:

This compound is nitrotrimesoyl chloride (NTMC) and is not availablecommercially.

A fourth compound is represented as follows:

This compound is perchlorotrimesoyl chloride (PCTMC), and is notavailable commercially.

A fifth compound is represented as follows:

This compound is 1,3,5-benzenetri-(difluoroacetoyl chloride), or BTFAC,and is not available commercially.

The first four of the above compounds have in common the TMC moleculewith electron-withdrawing from fluoro, chloro or nitro groups. The lastcompound may also be effective for the reasons given above. Further, inorder to provide the highly cross linked polymer system, difunctionalacid chlorides such as 5-fluoro-isophthalic acid chloride and tri- ortetra-functional amines may also be used. This is discussed in moredetail below.

On the amine side, the industrial standard MPD may continue to be asatisfactory amine and no additional candidates may be needed. On theother hand, other amines may also be used. In this regard, the followingare considered candidates for use because they are multifunctional whichprovides sterics and simpler acid chlorides such as 5-fluoro-isophthalicacid chloride. Also, some of the following examples do not require thearomatic ring, hence there is no N-ring chlorination. It will beunderstood that mixtures of the following amines may also be used.

A first example is represented as follows:

This compound is 1,3,5-triaminobenzene. The salt is availablecommercially and the free amine was synthesized by the applicants.

A second example is represented as follows:

This compound is 1,2,4,5-tetraaminobenzene, and is not availablecommercially.

Further amines are of interest in that they use an aliphatic ringsystem, which may prevent ring substation by chlorine.

A first amine of this type is represented as follows:

This compound is 1,2,3,4-tetraaminocyclohexane, and is not availablecommercially.

A second amine of this type is represented as follows:

This compound is tetrakis (aminomethyl) methane, and is not availablecommercially today.

As was mentioned above, these amines have more than two functionalgroups and thus can be used to make membranes that use a difunctionalacid chloride. These acid chlorides are generally easier to synthesize.

As discussed above, the major thrust of the invention concernsmodifications on the acid side of the polymer. As mentioned previously,the groups that are added to the TMC molecule are electron-withdrawing.With this approach, there may be no need to change from MPD on the amineside. This change makes practical sense for a number of reasons. In thisregard, for acid chlorides, where electron withdrawing groups are added,the following has been observed: (1) it is relatively easy to obtain orsynthesize di-functional or tri-functional acid chlorides; (2) there isan increase in electron-withdrawing away from the nitrogen; (3) thereare no solubility problems in hexane; (4) higher reactivity occursduring interfacial polymerization; (5) data on at least two membranesystems show excellent transport properties, particularly flux; and (6)a more hydrophobic acid chloride results.

In contrast, on the amine side, when attempting to addelectron-withdrawing groups, there are a number of problems, includingthe following: (1) difficulties in obtaining the precursors and overallsynthesis; (2) an increase in electron-withdrawing away from thenitrogen; (3) resonance problems resulting in ring chlorination; (4)water solubility problems arising from the addition of hydrophobicgroups; (5) less reactivity during interfacial polymerization; and (6)all successful membranes made based on the amine modification showproblems with flux.

It is also noted that although the prior art discloses amines such as5-chloro-m-phylenediamine, these amines are generally undesirable forthe purposes of the present invention, for the reasons discussed above.In addition, test data shows that amides made with5-chloro-m-phylenediamine actually degrade with chlorine. The rate ofdegradation may be less than with the MPD, which may improve membranelife in chlorinated waters, but these membranes are at best only amodest improvement. As mentioned above, there are also flux problemswith these 5-chloro-m-phylenediamine membranes.

Using the chemical principles described above, acid chlorides with theabove-mentioned modifications could be taken from the above examples (orfrom others that would be obvious to the routineer chemist) and thestandard amine, MPD to produce a chlorine resistant polyamide. Also,other amines could be taken from the above examples (or others that arenot mentioned but would be obvious to the routineer chemist) and couldbe part of the successful polymer.

In the examples that follow, a new class of polyamides are discussedthat are chlorine resistant. It will be appreciated that because of thischlorine resistance, applications of this polymer extend beyondmembranes into many other kinds of applications for the polymer.

It will also be understood that it is not possible to predict which acidchlorides and amines can be used to make membranes and, in particular,successful membranes, and that not all acid chlorides and amines can beused to make membranes. Thus, the invention represents a quitefortuitous finding of the right combination of these acid chlorides andamines that can be used to make membranes, and not just membranes, butsuccessful membranes with good transport properties of salt rejectionand flux.

As described above, one aspect of the invention concerns modifyingpolyamide polymers so that they exhibit chemical stability in chlorinewater environments. Because of the difficulty in obtaining chemical datafrom polymers, especially highly-cross linked polymer systems, Examples1 and 2 below began with the syntheses of amides. These amides were thenexposed to high concentrations of chlorinated water. It will beappreciated that these amides are the smaller units; polyamides arecomposed of many amide units. However, the chemical principles of theseamides that have been found apply directly to polyamide polymers.

Example 1

The amides described below were synthesized and exposed to chlorinatedwater. It is noted that the chlorine concentrations were high toaccelerate the degradation. In fact, if the actual application were ROmembranes, this would be the equivalent of 1.2×10⁵ or 2.4×10⁵ ppm-hrs ofchlorine over the period of 24 or 48 hours. These chlorine exposures areapproximately what RO membranes would receive after 13.7 or 27.4 yearsof operation at 1.0 mg/L chlorine, and this would be well beyond thelife of RO membranes currently in use. Nuclear Magnetic Resonanceanalysis was done using a Varian, Mercury 400 MHz instrument.Considering this example in more detail the following amides weresynthesized:

These compounds were then subjected to the high concentrations ofchlorine mentioned above in order to accelerate the degradation.

Nuclear Magnetic Resonance (NMR) and ATR-IR data on these samples beforeand after the accelerated chlorination tests show chlorine degradationon amides 2, 4 and 6. On the other hand, amides 1, 3 and 5 did notchlorinate.

It is believed that the nitro groups are electron-withdrawing because ofthe π bonds to the electronegative oxygen atoms. The amino groups arenot electron-withdrawing and this explains why half of the above amidesare chlorine resistant and the other half degrade. These changes were onthe amine side. For membranes made by interfacial polymerization, thenext example shows changes on the acid side.

Example 2

This example provides additional data on chlorine resistant amides.

As in the previous example, these compounds were then subjected to highconcentrations of chlorine to accelerate the degradation. As discussedabove, if the application were RO membranes, this would be theequivalent of 1.2×10⁵ or 2.4×10⁵ ppm-hrs of chlorine over the period of24 or 48 hours, and these chlorine exposures are approximately what ROmembranes would receive after 13.7 or 27.4 years of operation at 1.0mg/L chlorine. ¹H-NMR analysis was done using a Varian, Mercury 400 MHzinstrument. All samples were dissolved in DMSO-d6 with 0.01% TMS.

In this example, the control is N-[3-(benzoylamino)phenyl]benzamide,represented below:

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern4 N—H 10.29 2 s 1 Ar—H 8.32 1 s 5 Ar—H 7.94 4 dd 2, 6, 7 Ar—H 7.57-7.478 m 3 Ar—H 7.3 1 t

For chlorine-treated, N-[3-(benzoylamino)phenyl]benzamide, the followingresults were obtained.

Number Chemical of Assignment Type shift (ppm) protons Splitting patternN—H 10.45, 10.20, 10.13, 30% s 10.08 4 N—H 10.29 70% s 1 Ar—H  8.32 sAr—H 8.10, 8.00 s, s 5 Ar—H  7.94 dd Ar—H 7.85, 7.75 dd, dd 2, 6, 7 andAr—H 7.65-7.45 Altered multiple other

The NMR data indicates the molecular structure of the above amide sampleunder investigation has changed significantly on exposure to chlorinewater. The four additional N-H signals from the exposed sample suggestthat there are at least four different aromatic ring chlorinated speciesaccounting for about 30% of the original compound.

Example 3

In this example, the control was 4-fluoro-N-{[3-(4-fluorobensoyl)amino]phenyl}benzamide, represented below:

The following results were obtained for the NMR testing:

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern4 N—H 10.39 2 s 1 Ar—H 8.9 1 s 6 Ar—H 8.04 4 dd 2 Ar—H 7.48 2 dd 5, 3Ar—H 7.37 5 m

For chlorine-treated,4-fluoro-N-{[3-(4-fluorobensoyl)amino]phenyl}benzamide, the followingresults were obtained.

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern4 N—H 10.39 2 S 1 Ar—H 8.9 1 S 6 Ar—H 8.04 4 Dd 2 Ar—H 7.48 2 Dd 5, 3Ar—H 7.37 5 M

Example 4

In this example, the control is 5-fluoro-(N,N′-diphenyl)isophthalamide,represented below:

The following results for the NMR testing were obtained for the control.

Chemical  Number of Assignment  Type  shift (ppm) protons Splittingpattern 3 N—H 10.52 2 S 1 Ar—H 8.42 1 S 2 Ar—H 8.00 2 d 4 Ar—H 7.98 4 d5 Ar—H 7.38 4 t 6 Ar—H 7.13 2 t

For the chlorine treated, 5-fluoro-(N,N′-diphenyl)isophthalamide, theNMR testing produced the following results:

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern3 N—H 10.52 2 s 1 Ar—H 8.42 1 s 2 Ar—H 8.00 2 d 4 Ar—H 7.98 4 d 5 Ar—H7.38 4 t 6 Ar—H 7.13 2 t

The NMR data clearly indicates that the amide under investigation isunaffected by chlorine.

Example 5

In this example, the control was2,4,5,6-tetrafluoro-(N,N′-diphenyl)isophthalamide, represented below:

The NMR testing produced the following results:

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern1 N—H 11.00 2 s 2 Ar—H 7.67 4 d 3 Ar—H 7.390 4 t 4 Ar—H 7.17 2 t

The following results were obtained for Cl-treated,2,4,5,6-tetrafluoro-(N,N′-diphenyl)isophthalamide.

Chemical Number of Assignment Type shift (ppm) protons Splitting pattern1 N—H 11.00 2 s 2 Ar—H 7.67 4 d 3 Ar—H 7.390 4 t 4 Ar—H 7.17 2 t

Again, the NMR data shows that this particular amide is not affected bychlorine.

It is believed to be evident from the foregoing Examples 2 to 6 that theinvention is not limited to these specific chlorine resistant amides andcan be extended to other polyamide polymers that would be chlorineresistant given that the same chemical principles discussed above wouldbe involved. As discussed above, the changes made to the amides in theseexamples are on the acid side.

As mentioned above, the discovery that membranes can be made from atleast one of the examples is highly significant. Using the polymersystem composed of monofluorotrimesoyl chloride (MFTMC) andm-phenylenediamine (MPD), the inventors were able to make use of thechemical principle of providing sufficient electron-withdrawing from theacid to the amide bond and the amine. This electron-withdrawingeffectively deactivates the nitrogen so as to prevent N-chlorination andring chlorination. This makes possible a modification that is relativelyeasy to synthesize, allows sufficient solubility in the organic phaseduring interfacial polymerization, provides a higher reactivity duringinterfacial polymerization, and achieves most of all the desiredtransport properties.

An example will now be considered of membranes made from MFTMC and MPD,demonstrating the good transport properties of such membranes.

Example 6

A MFTTMC and MPD membrane was tested and was found to have goodtransport properties on seawater (13.1 gpd and 98.4% salt rejection).The results are set forth below.

    Row No.       Membrane ID Solution A, amine/water solution, (pH)Solution A, amine/water solution (Conc. wt-%) Solution B, acid chloride/hexane solution (Conc. wt-%) $\begin{matrix}~ \\\frac{{Reverse}\mspace{14mu} {osmosis}\mspace{14mu} {performance}}{{Water}\mspace{14mu} {flux}\mspace{14mu} ({gfd})\mspace{14mu} {rejection}\mspace{14mu} (\%)}\end{matrix}\quad$ 2. BBCR-1219-5FTMC — 4 wt-% MPD MFTMC = 0.15% 13.198.4

This result is very promising. Moreover, these transport properties areexpected to improve in time with improvements in, i.e., modificationsto, the monomer purity and casting techniques.

A further example will be considered below which provides long-termfield test data in connection with the membranes.

Example 7

In the following example, the tests results provide a comparison of theMFTMC and MPD membranes with commercial controls. FIG. 1 is a plot ofwater flux as a function of time while FIG. 2 is a plot of saltrejection as a function of time.

In FIG. 1, #3 and #8 are commercial controls made with the standardTMC/MPD monomers. All of the other data is for the MFTMC/MPD membranes.While the flux and salt rejection remains relatively constant for thecontrols over this period, the expected decrease in salt rejection, andeither an increase or decrease in flux for the controls, can be expectedin the months ahead. The MTFTMC and MPD membranes continue to provide asalt barrier over these months similar to the controls. Further, thesemembranes show higher flux than the controls and one of the membranesshows an increase in salt rejection over this period.

Other successful membranes were made from the class of compoundsdescribed above.

Example 8

In this example, the following membrane system was made which is basedon the above principles:

The tetra amine provides the needed cross-linking with the difunctionalacid chloride. Also, the non-aromatic amine prevents ring chlorinationand the electron-withdrawing from the acid side stops amide nitrogenchlorination. A first membrane was produced having good transportproperties on seawater (19.3 gpd and 98.7% salt rejection). A secondmembrane had even better flux as indicated:

    Row No.       Membrane ID Solution A, amine/water solution, (pH)Solution A, amine/water solution (Conc. wt-%) Solution B, acid chloride/hexane solution (Conc. wt-%) $~{\begin{matrix}{~~} \\{~\frac{{Reverse}\mspace{14mu} {osmosis}\mspace{14mu} {performance}}{{Water}\mspace{14mu} {flux}\mspace{14mu} ({gfd})\mspace{14mu} {rejection}\mspace{14mu} (\%)}}\end{matrix}\quad}$ 3. BBCR-1207-237- 5NIPCAC — 4 wt-% tetrakis(aminomethyl) methane 5-nitro-isophthalic acid chloride = 0.15% 22.298.3

The excellent results produced are highly significant and quiteunexpected, i.e. it would not be expected that the membrane wouldexhibit both strong chlorine resistance and good flux. Tetrakis(methylamino methyl) methane can also be used.

In the examples discussed above, electron-withdrawing groups are locatedon the 6-member aromatic ring system of the acid chloride molecule andan amines such as the industrial standard MPD is used. These arepreferred embodiments. However, it will be understood that polyaminesand, in particular, polyamines containing aminobenzene would also beincluded. Moreover, as indicated previously, there are other examplesthat fall within the scope of the invention and others that may do so.Consider the following figure:

If “X” represents an electron withdrawing group, then by substitutingone or both of the hydrogen(s) on the above methylene group between theacid chloride ring system and the acid chloride group, the acid side ofthe polymer will withdraw electrons away from the amide nitrogen atomthereby creating chlorine resistance. Of course, this adjustment can bemade on all acid chloride groups per ring.

Further, acid chlorides could be made from aliphatic rings systems thatare 3, 4, 5, 6, or 7 carbon units in size. Below are two examples.

In these acid chlorides, the electron withdrawing function would beachieved by induction away from the amide nitrogen atom to therebycreate chlorine resistance. The ring(s) could be partially substitutedwith “X” or fully substituted.

Although the focus in the principal examples set forth above is onsynthesizing and purifying cis, trans, cis, transcyclopentanetetracarboxylic acid chloride, using the just describedapproach, a single fluoro group could be added anywhere on the ringsystem to create chlorine resistance. However, it may be necessary tohave more than one such group, or to completely substitute all thehydrogen on the ring with fluorine.

Methylene groups between the ring(s) and acid chloride groups may alsobe useful in creating chlorine resistance. This is a similar approachthat follows from the first example.

A non-ring based acid chloride is another candidate. The followingexample is of interest:

In membrane applications, membranes have been made using tetrakis(aminomethyl) methane as an amine with a similar structure.

As will be apparent from the foregoing, one key aspect of the inventionconcerns electron-withdrawing away from the amide nitrogen by modifyingthe acid chloride molecule with electron-withdrawing groups. A number ofmonomers have been identified that result in, or can be predicted toresult in, membranes with desirable transport properties.

Although as discussed above, and as is also discussed below, theinvention has many different applications, one important application isin the manufacture of reverse osmosis (RO) membranes. Referring to FIG.3, a spiral-wound RO membrane unit 10 is shown which is typical of thosecurrently used in desalting plants. The unit 10 includes a membraneelement 12 which is constructed in accordance with the presentinvention. Because element 10 is conventional apart from membrane 12(and moreover, in this regard, the external physical appearance ofmembrane 12 would not be different for a conventional membrane), unit 10will be only briefly described below by way of background. It will alsobe understood that membranes made by the methods of the presentinvention can be used in different membrane units than that shown inFIG. 1.

The unit 10 includes an outer pressure vessel 14 typically made offiberglass with an antitelescoping device or shell 16 at opposite endsthereof. An axially extending product tube 18 is located centrally ofelement 10, as shown. The membrane element 12 itself includes a saltrejecting membrane surface 12 a which forms part of a membrane leaf 12 bincluding a tricot spacer 12 c, a mesh spacer 12 d and a membrane 12 e.It will be appreciated that the membrane element 12 is the key componentof unit 10 and defines the actual surface where salt is separated fromwater. In embodiments of the invention, the membrane would be made froma chlorine resistant PA polymer, as described above.

It will be appreciated that chlorine resistant PA polymers should find awide range of application in industry. Applications could include linearand highly cross-linked polyamide polymers for the production of pipes,tanks, and the like, fibers in clothing, chemically resistant coatings,flame retardant materials (due to the fluoro groups), and chlorineresistant surfactants. Further, even in the area of membranes there ismore than RO, and filtering processes such as microfiltration (MF),nanofiltration (NF), and ultrafiltration (UF) could all benefit from PApolymers having improved chlorine resistance.

Although the invention has been described above in relation to preferredembodiments thereof, it will be understood by those skilled in the artthat variations and modifications can be effected in these preferredembodiments without departing from the scope and spirit of theinvention.

1. A non-ionizing acid chloride monomer modified withelectron-withdrawing groups that exhibit sufficient activity to (i)minimize any chlorination of an acid group and an amine group on apolyamide, and (ii) minimize N-chorination on a polyamide.
 2. The acidchloride monomer as claimed in claim 1 wherein said electron-withdrawinggroups are selected from the group consisting of fluoro, chloro, nitrogroups and mixtures thereof.
 3. The non-ionizing acid chloride monomerof claim 1 is monofluorotrimesoyl chloride.
 4. The non-ionizing acidchloride monomer of claim 1 is perfluorotrimesoyl chloride.
 5. Thenon-ionizing acid chloride monomer of claim 1 is nitrotimesoyl chloride.6. The non-ionizing acid chloride monomer of claim 1 is1,3,5-benzenetri-(difluoroacetoyl chloride).
 7. A chlorine resistantpolyamide comprising the reaction product of an amine and the acidchloride monomer of claim 1, wherein the acid chloride monomer ismodified with electron-withdrawing groups that exhibit sufficientactivity to (i) minimize any chlorination on both the amine and acidchloride side and (ii) minimize N-chlorination.
 8. The chlorineresistant polyamide of claim 7, wherein the acid chloride monomer ismonofluorotrimesoyl chloride.
 9. The chlorine resistant polyamide ofclaim 8, wherein the amine is tetrakis (aminomethyl) methane.
 10. Thechlorine resistant polyamide of claim 7, wherein the acid chloridemonomer is perfluorotrimesoyl chloride.
 11. The chlorine resistantpolyamide of claim 7, wherein the acid chloride monomer isnitrotrimesoyl chloride.
 12. The chlorine resistant polyamide of claim7, wherein the acid chloride monomer is perchlorotrimesoyl chloride. 13.The chlorine resistant polyamide of claim 7, wherein the acid chloridemonomer is 1,3,5-benzenetri-(difluoroacetoyl chloride).
 14. The chlorineresistant polyamide of claim 7, wherein the amine is m-phenylenediamine.15. The chlorine resistant polyamide of claim 7, wherein the amine is1,3,5-triaminobenzene.
 16. The chlorine resistant polyamide of claim 7,wherein the amine is 1,2,4,5-tetraaminobenzene.
 17. The chlorineresistant polyamide of claim 7, wherein the amine is1,2,3,4-tetraaminocyclohexane.
 18. The chlorine resistant polyamide ofclaim 7, wherein the amine is tetrakis (aminomethyl)methane.
 19. Achlorine resistant polyamide comprising the reaction product of an amineand an acid chloride monomer wherein the acid chloride monomer ismodified with electron-withdrawing groups that exhibit sufficientactivity to (i) minimize any chlorination on both the amine and acidchloride side and (ii) minimize N-chlorination.
 20. The chlorineresistant polyamide of claim 19, wherein the acid chloride monomer ismonofluorotrimesoyl chloride.
 21. The chlorine resistant polyamide ofclaim 19, wherein the acid chloride monomer is perfluorotrimesoylchloride.
 22. The chlorine resistant polyamide of claim 19, wherein theacid chloride monomer is nitrotrimesoyl chloride.
 23. The chlorineresistant polyamide of claim 19, wherein the acid chloride monomer isperchlorotrimesoyl chloride.
 24. The chlorine resistant polyamide ofclaim 19, wherein the acid chloride monomer is1,3,5-benzenetri-(difluoroacetoyl chloride).
 25. The chlorine resistantpolyamide of claim 19, wherein the amine is m-phenylenediamine.
 26. Thechlorine resistant polyamide of claim 19, wherein the amine is1,3,5-triaminobenzene.
 27. The chlorine resistant polyamide of claim 19,wherein the amine is 1,2,4,5-tetraaminobenzene.
 28. The chlorineresistant polyamide of claim 19, wherein the amine is1,2,3,4-tetraaminocyclohexane.
 29. The chlorine resistant polyamide ofclaim 19, wherein the amine is tetrakis (aminomethyl) methane.
 30. Thechlorine resistant polyamide of claim 20, wherein the amine is tetrakis(aminomethyl) methane.
 31. A reverse osmosis desalination unitcomprising a membrane support and, mounted on the membrane support, achlorine resistant membrane including a chlorine resistant polyamidecomprising the reaction product of an amine and an acid chloride monomerwherein the acid chloride monomer is modified with electron-withdrawinggroups that exhibit sufficient activity to (i) minimize any chlorinationon both the amine and acid chloride side and (ii) minimizeN-chlorination.
 32. The desalination unit of claim 31, wherein the acidchloride monomer is monofluorotrimesoyl chloride.
 33. The desalinationunit of claim 31, wherein the acid chloride monomer isperfluorotrimesoyl chloride.
 34. The desalination unit of claim 31,wherein the acid chloride monomer is nitrotrimesoyl chloride.
 35. Thedesalination unit of claim 31, wherein the acid chloride monomer isperchlorotrimesoyl chloride.
 36. The desalination unit of claim 31,wherein the acid chloride monomer is 1,3,5-benzenetri-(difluoroacetoylchloride).